U.S. patent number 6,573,359 [Application Number 10/017,612] was granted by the patent office on 2003-06-03 for methods of post-polymerization injection in condensation polymer production.
This patent grant is currently assigned to Wellman, Inc.. Invention is credited to Walter Lee Edwards, Tony Clifford Moore, Carl Steven Nichols, Robert Joseph Schiavone.
United States Patent |
6,573,359 |
Nichols , et al. |
June 3, 2003 |
**Please see images for:
( Certificate of Correction ) ** |
Methods of post-polymerization injection in condensation polymer
production
Abstract
The invention is a novel method for the late introduction of
additives into a process for making condensation polymers. The
method employs a reactive carrier that functions as a delivery
vehicle for one or more additives. The reactive carrier reacts with
the condensation polymers, thereby binding the reactive carrier in
the polymer resin and preventing the emergence of the reactive
carrier from the polymer resin during subsequent thermal
processing.
Inventors: |
Nichols; Carl Steven (Waxhaw,
NC), Moore; Tony Clifford (Charlotte, NC), Schiavone;
Robert Joseph (Matthews, NC), Edwards; Walter Lee
(Harrisburg, NC) |
Assignee: |
Wellman, Inc. (Shrewsbury,
NJ)
|
Family
ID: |
27360838 |
Appl.
No.: |
10/017,612 |
Filed: |
December 14, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
932150 |
Aug 17, 2001 |
|
|
|
|
738150 |
Dec 15, 2000 |
|
|
|
|
Current U.S.
Class: |
528/491;
264/176.1; 264/209.1; 264/464; 428/35.7; 428/36.3; 428/364;
524/115; 524/81; 525/437; 526/65; 526/66; 528/486; 528/487;
528/489; 528/503 |
Current CPC
Class: |
C08G
63/78 (20130101); C08G 63/80 (20130101); C08G
63/91 (20130101); C08G 64/20 (20130101); C08G
64/42 (20130101); C08G 69/04 (20130101); C08G
69/28 (20130101); C08G 69/48 (20130101); C08J
3/2056 (20130101); C08J 3/226 (20130101); C08L
67/02 (20130101); C08L 67/02 (20130101); C08L
71/00 (20130101); B29K 2105/0002 (20130101); C08J
2367/02 (20130101); Y10T 428/1369 (20150115); Y10T
428/1352 (20150115); Y10T 428/2913 (20150115) |
Current International
Class: |
C08G
64/42 (20060101); C08G 63/80 (20060101); C08G
64/20 (20060101); C08J 3/20 (20060101); C08J
3/22 (20060101); C08J 3/205 (20060101); C08G
63/00 (20060101); C08G 64/00 (20060101); C08G
69/28 (20060101); C08G 69/04 (20060101); C08G
63/91 (20060101); C08G 63/78 (20060101); C08G
69/00 (20060101); C08G 69/48 (20060101); C08L
67/02 (20060101); C08L 67/00 (20060101); C08F
006/00 () |
Field of
Search: |
;528/486,487,489,491,503
;525/437 ;524/81,115 ;428/35.7,36.3,364 ;264/176.1,209.1,464
;526/65,66 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 169 085 |
|
Jan 1986 |
|
EP |
|
0 272 417 |
|
Jun 1988 |
|
EP |
|
0 455 370 |
|
Nov 1991 |
|
EP |
|
0 703 263 |
|
Mar 1996 |
|
EP |
|
0 718 341 |
|
Jun 1996 |
|
EP |
|
61-250034 |
|
Nov 1986 |
|
JP |
|
0309348 |
|
Feb 1991 |
|
JP |
|
08120066 |
|
May 1996 |
|
JP |
|
11323126 |
|
Nov 1999 |
|
JP |
|
WO 99/41297 |
|
Aug 1999 |
|
WO |
|
WO 00/12783 |
|
Mar 2000 |
|
WO |
|
WO 00/66659 |
|
Nov 2000 |
|
WO |
|
WO 02/16464 |
|
Feb 2002 |
|
WO |
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Summa & Allan, P.A.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. application Ser.
No. 09/932,150, for Methods of Post-Polymerization Extruder
Injection In Polyethylene Terephthalate Production, filed Aug. 17,
2001, which itself is a continuation-in-part of copending and
commonly-assigned U.S. application Ser. No. 09/738,150, for Methods
of Post-Polymerization Injection in Continuous Polyethylene
Terephthalate Production, filed Dec. 15, 2000. This application is
also related to concurrently-filed application Ser. No. 10/017,400
for Methods of Post-Polymerization Extruder Injection in
Condensation Polymer Production. Each of these pending applications
is commonly assigned with this application and is hereby
incorporated entirely herein by reference.
Claims
That which is claimed is:
1. A method for introducing additives into a process for making
condensation polymers, comprising: polymerizing oligomeric
precursors via melt phase polycondensation to form condensation
polymers having carbonyl functionality; and thereafter introducing
into the condensation polymers a reactive carrier having a
molecular weight of less than about 10,000 g/mol, the reactive
carrier being the delivery vehicle for one or more additives.
2. A method according to claim 1, wherein the step of polymerizing
oligomeric precursors comprises polymerizing the oligomeric
precursors via melt phase polycondensation to form condensation
polymers having carbonyl functionality and a target average degree
of polymerization of at least about 70; and further comprising
completing the melt phase polycondensation of the condensation
polymers after the step of introducing the reactive carrier into
the condensation polymers.
3. A method according to claim 1, further comprising reacting a
first polyfunctional component and a second polyfunctional
component to form oligomeric precursors to condensation polymers,
prior to the step of polymerizing the oligomeric precursors via
melt phase polycondensation.
4. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diacids and diols to form the
oligomeric precursors.
5. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diesters and diols to form the
oligomeric precursors.
6. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diols and derivatives of carbonic acid
to form the oligomeric precursors.
7. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diisocyanates and diols to form the
oligomeric precursors.
8. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diacids and diamines to form the
oligomeric precursors.
9. A method according to claim 3, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting dianhydrides and diamines to form the
oligomeric precursors.
10. A method according to claim 1, wherein the step of polymerizing
the oligomeric precursors via melt phase polycondensation comprises
self-polymerizing monomers possessing multi-functionality to yield
condensation polymers having carbonyl functionality.
11. A method according to claim 1, further comprising forming the
condensation polymers and the reactive carrier into chips or
pellets.
12. A method according to claim 1, further comprising solid state
polymerizing the condensation polymers and the reactive
carrier.
13. A method according to claim 1, further comprising forming the
condensation polymers and the reactive carrier into containers.
14. A method according to claim 1, further comprising spinning the
condensation polymers and the reactive carrier into fibers.
15. A method according to claim 1, further comprising forming the
condensation polymers and the reactive carrier into films.
16. A method according to claim 1, wherein the condensation
polymers comprise a polyester.
17. A method according to claim 1, wherein the condensation
polymers comprise a polyurethane.
18. A method according to claim 1, wherein the condensation
polymers comprise a polycarbonate.
19. A method according to claim 1, wherein the condensation
polymers comprise a polyamide.
20. A method according to claim 1, wherein the condensation
polymers comprise a polyimide.
21. A method according to claim 1, wherein the reactive carrier is
a liquid or slurry at about 100.degree. C.
22. A method according to claim 1, wherein the reactive carrier is
a liquid or slurry at near ambient temperatures.
23. A method according to claim 1, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that
bulk polymer properties of the condensation polymers are not
significantly affected.
24. A method according to claim 1, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the condensation polymers is less than about
10,000 ppm.
25. A method according to claim 1, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the condensation polymers is less than about 1000
ppm.
26. A method according to claim 1, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the condensation polymers is less than 500
ppm.
27. A method according to claim 1, wherein the reactive carrier has
a molecular weight of less than about 6000 g/mol.
28. A method according to claim 1, wherein the reactive carrier has
a molecular weight of less than about 4000 g/mol.
29. A method according to claim 1, wherein the reactive carrier has
a molecular weight of between about 300 and 2000 g/mol.
30. A method according to claim 1, wherein the reactive carrier has
a molecular weight of between about 400 and 1000 g/mol.
31. A method according to claim 1, wherein the reactive carrier
comprises a polyol.
32. A method according to claim 1, wherein the reactive carrier
comprises a polyol having a molecular weight of between about 300
and 2000 g/mol.
33. A method according to claim 1, wherein the reactive carrier
comprises a polyol having a molecular weight of between about 400
and 1000 g/mol.
34. A method according to claim 1, wherein the reactive carrier
comprises polyethylene glycol.
35. A method according to claim 1, wherein the reactive carrier is
selected from the group consisting of dimer acids, dimer
anhydrides, trimer acids, and trimer anhydrides.
36. A method according to claim 1, wherein the reactive carrier is
a derivative or either caprolactone or caprolactam.
37. A method according to claim 1, wherein the reactive carrier is
selected from the group consisting of esters, amides, imides,
amines, isocyanates, oxazolines, acids, and anhydrides.
38. A method according to claim 1, wherein the one or more
additives comprise a UV absorber.
39. A method according to claim 1, wherein the one or more
additives comprise an additive that increases preform heat-up
rate.
40. A method according to claim 1, wherein the one or more
additives comprise a phosphorous-containing stabilizer.
41. A method according to claim 1, wherein the one or more
additives comprise an oxygen scavenger.
42. A method according to claim 1, wherein the one or more
additives comprise an exfoliated clay nanocomposite.
43. A method according to claim 1, wherein the one or more
additives comprise between about 20 and 200 ppm of an inert
particulate additive selected from the group consisting of talc and
calcium carbonate, the inert particulate additive having an average
particle size of less than about ten microns.
44. A method according to claim 43, wherein the inert particulate
additive is surface-modified.
45. A method according to claim 1, wherein the one or more
additives include an additive selected from the group consisting of
friction-reducing additives, stabilizers, inert particulate
additives, colorants, antioxidants, branching agents, barrier
agents, flame retardants, crystallization control agents,
acetaldehyde reducing agents, impact modifiers, catalyst
deactivators, melt strength enhancers, anti-static agents,
lubricants, chain extenders, nucleating agents, solvents, fillers,
and plasticizers.
46. A method for introducing additives into a process for making
condensation polymers, comprising: polymerizing oligomeric
precursors via melt phase polycondensation to form condensation
polymers having carbonyl functionality and a target average degree
of polymerization of at least about 70; then, after the
condensation polymers have achieved the target average degree of
polymerization, introducing into the condensation polymers a
reactive carrier having a molecular weight of less than about
10,000 g/mol, the reactive carrier being the delivery vehicle for
one or more additives; and thereafter completing the melt phase
polycondensation of the condensation polymers.
47. A method according to claim 46, wherein the target average
degree of polymerization of the condensation polymers is at least
about 80.
48. A method according to claim 46, wherein the target average
degree of polymerization of the condensation polymers is at least
about 90.
49. A method according to claim 46, wherein the target average
degree of polymerization of the condensation polymers is at least
about 100.
50. A method according to claim 46, further comprising forming the
condensation polymers and the reactive carrier into chips or
pellets.
51. A method according to claim 46, further comprising solid state
polymerizing the condensation polymers and the reactive
carrier.
52. A method according to claim 46, further comprising forming the
condensation polymers and the reactive carrier into containers,
fibers, or films.
53. A method according to claim 46, wherein the condensation
polymers comprise a polyester.
54. A method according to claim 46, wherein the condensation
polymers comprise a polyurethane.
55. A method according to claim 46, wherein the condensation
polymers comprise a polycarbonate.
56. A method according to claim 46, wherein the condensation
polymers comprise a polyamide.
57. A method according to claim 46, wherein the condensation
polymers comprise a polyimide.
58. A method according to claim 46, wherein the reactive carrier is
a liquid or slurry at near ambient temperatures.
59. A method according to claim 46, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the polymers is less than about 10,000 ppm.
60. A method according to claim 46, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the polymers is less than about 1000 ppm.
61. A method according to claim 46, wherein the reactive carrier
has a molecular weight of less than about 6000 g/mol.
62. A method according to claim 46, wherein the reactive carrier
has a molecular weight of between about 300 and 2000 g/mol.
63. A method according to claim 46, wherein the reactive carrier
has a molecular weight of between about 400 and 1000 g/mol.
64. A method according to claim 46, wherein the reactive carrier
comprises a polyol.
65. A method according to claim 46, wherein the reactive carrier is
selected from the group consisting of esters, amides, imides,
amines, isocyanates, oxazolines, acids, and anhydrides, the
reactive carrier being capable of reacting with the condensation
polymers during solid state polymerization and not causing the
condensation polymers to suffer loss of molecular weight during
subsequent heated polymer processes.
66. A method according to claim 46, wherein the one or more
additives comprise a UV absorber.
67. A method according to claim 46, wherein the one or more
additives comprise between about 20 and 200 ppm of a
surface-modified, inert particulate additive selected from the
group consisting of talc and calcium carbonate, the inert
particulate additive having an average particle size of less than
about ten microns.
68. A method according to claim 46, wherein the one or more
additives include an additive selected from the group consisting of
an additive that increases preform heat-up rate, a
phosphorous-containing stabilizer, an oxygen scavenger, and an
exfoliated clay nanocomposite.
69. A method according to claim 46, wherein the one or more
additives include an additive selected from the group consisting of
friction-reducing additives, stabilizers, inert particulate
additives, colorants, antioxidants, branching agents, barrier
agents, flame retardants, crystallization control agents,
acetaldehyde reducing agents, impact modifiers, catalyst
deactivators, melt strength enhancers, anti-static agents,
lubricants, chain extenders, nucleating agents, solvents, fillers,
and plasticizers.
70. A method for introducing additives into a process for making
condensation polymers, comprising: reacting a first polyfunctional
component and a second polyfunctional component to form oligomeric
precursors to condensation polymers; polymerizing the oligomeric
precursors via melt phase polycondensation to form condensation
polymers having carbonyl functionality; and thereafter introducing
into the condensation polymers a reactive carrier having a
molecular weight of less than about 10,000 g/mol, the reactive
carrier being the delivery vehicle for one or more additives.
71. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diacids and diols to form the
oligomeric precursors.
72. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diesters and diols to form the
oligomeric precursors.
73. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diols and derivatives of carbonic acid
to form the oligomeric precursors.
74. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diisocyanates and diols to form the
oligomeric precursors.
75. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting diacids and diamines to form the
oligomeric precursors.
76. A method according to claim 70, wherein the step of reacting a
first polyfunctional component and a second polyfunctional
component comprises reacting dianhydrides and diamines to form the
oligomeric precursors.
77. A method according to claim 70, further comprising forming the
condensation polymers into chips or pellets.
78. A method according to claim 70, further comprising: pelletizing
the condensation polymers; and solid state polymerizing the
condensation polymers and the reactive carrier.
79. A method according to claim 70, further comprising forming the
condensation polymers into containers, fibers, or films.
80. A method according to claim 70, wherein the reactive carrier is
a liquid or slurry at about 100.degree. C.
81. A method according to claim 70, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that
bulk polymer properties of the condensation polymers are not
significantly affected.
82. A method according to claim 70, wherein the reactive carrier is
introduced to the condensation polymers in quantities such that its
concentration in the condensation polymers is less than about 1000
ppm.
83. A method according to claim 70, wherein the reactive carrier
has a molecular weight of less than about 6000 g/mol.
84. A method according to claim 70, wherein the reactive carrier
has a molecular weight of between about 300 and 2000 g/mol.
85. A method according to claim 70, wherein the reactive carrier
comprises a polyol having a molecular weight that is sufficiently
high such that the polyol will not substantially reduce the average
molecular weight of the condensation polymers.
86. A method according to claim 70, wherein the reactive carrier is
selected from the group consisting of esters, amides, imides,
amines, isocyanates, oxazolines, acids, and anhydrides, the
reactive carrier being capable of reacting with the condensation
polymers during solid state polymerization and not causing the
condensation polymers to suffer loss of molecular weight during
subsequent heated polymer processes.
87. A method according to claim 70, wherein the one or more
additives comprise between about 20 and 200 ppm of a
surface-modified, inert particulate additive selected from the
group consisting of talc and calcium carbonate, the inert
particulate additive having an average particle size of less than
about ten microns.
88. A method according to claim 70, wherein the one or more
additives include an additive selected from the group consisting of
UV absorbers, heat-up rate enhancers, friction-reducing additives,
stabilizers, inert particulate additives, colorants, antioxidants,
branching agents, barrier agents, oxygen scavengers, flame
retardants, crystallization control agents, acetaldehyde reducing
agents, impact modifiers, catalyst deactivators, melt strength
enhancers, anti-static agents, lubricants, chain extenders,
nucleating agents, solvents, fillers, and plasticizers.
Description
FIELD OF THE INVENTION
The present invention relates to the production of condensation
polymers. More particularly, the present invention relates to the
late introduction of additives into condensation polymers via
reactive carriers.
BACKGROUND OF THE INVENTION
Because of their strength, heat resistance, and chemical
resistance, polyester fibers and films are an integral component in
numerous consumer products manufactured worldwide. Most commercial
polyester used for polyester fibers and films is polyethylene
terephthalate (PET) polyester. Because polyethylene terephthalate
forms a lightweight and shatter proof product, another popular use
for polyethylene terephthalate is as a resin for containers,
especially beverage bottles.
Before 1965, the only feasible method of producing polyethylene
terephthalate polyester was to use dimethyl terephthalate (DMT). In
this technique, dimethyl terephthalate and ethylene glycol are
reacted in a catalyzed ester interchange reaction to form
bis(2-hydroxyethyl) terephthalate monomers and oligomers, as well
as a methanol byproduct that is continuously removed. These
bis(2-hydroxyethyl)terephthalate monomers and oligomers are then
polymerized via polycondensation to produce polyethylene
terephthalate polymers.
Purer forms of terephthalic acid (TA) are now increasingly
available. Consequently, terephthalic acid has become an
acceptable, if not preferred, alternative to dimethyl terephthalate
as a starting material for the production of polyethylene
terephthalate. In this alternative technique, terephthalic acid and
ethylene glycol react in a generally uncatalyzed esterification
reaction to yield low molecular weight monomers and oligomers, as
well as a water byproduct that is continuously removed. As with the
dimethyl terephthalate technique, the monomers and oligomers are
subsequently polymerized by polycondensation to form polyethylene
terephthalate polyester. The resulting polyethylene terephthalate
polymer is substantially identical to the polyethylene
terephthalate polymer resulting from dimethyl terephthalate, albeit
with some end group differences.
Polyethylene terephthalate polyester may be produced in a batch
process, where the product of the ester interchange or
esterification reaction is formed in one vessel and then
transferred to a second vessel for polymerization. Generally, the
second vessel is agitated and the polymerization reaction is
continued until the power used by the agitator reaches a level
indicating that the polyester melt has achieved the desired
intrinsic viscosity and, thus, the desired molecular weight. More
commercially practicable, however, is to carry out the
esterification or ester interchange reactions, and then the
polymerization reaction as a continuous process. The continuous
production of polyethylene terephthalate results in greater
throughput, and so is more typical in large-scale manufacturing
facilities.
When the polymerization process is complete, the resulting polymer
melt is typically extruded and pelletized for convenient storage
and transportation before being transformed into specific polyester
articles (e.g., filament, films, or bottles). The latter kinds of
steps are herein referred to as "polyester processing."
In both batch and continuous processes, a high activity catalyst is
often employed to increase the rate of polymerization, thereby
increasing the throughput of the resulting polyethylene
terephthalate polyester. The high activity catalysts that are used
in the polymerization of polyethylene terephthalate polyester can
be basic, acidic, or neutral, and are often metal catalysts.
Primarily, the traditional polymerization catalysts used in the
formation of polyethylene terephthalate from both terephthalic acid
and dimethyl terephthalate contain antimony, most commonly antimony
trioxide (Sb.sub.2 O.sub.3). Although increasing production rates,
polymerization catalysts like antimony trioxide will eventually
begin to catalyze or encourage the degradation of the polyethylene
terephthalate polymer. Such polymer degradation results in the
formation of acetaldehyde, the discoloration (e.g., yellowing) of
the polyethylene terephthalate polyester, and reduction of polymer
molecular weight.
Furthermore, the recent availability of "hotter" catalysts that can
significantly increase throughput has generated a corresponding
need for better stabilization of the resulting polyester. U.S. Pat.
No. 5,008,230 for a Catalyst for Preparing High Clarity, Colorless
Polyethylene Terephthalate is exemplary of such an improved
catalyst. To reduce the degradation and discoloration of
polyethylene terephthalate polyester, stabilizing compounds are
used to sequester ("cool") the catalyst, thereby reducing its
effectiveness. The most commonly used stabilizers contain
phosphorous, typically in the form of phosphates and phosphites.
The phosphorous-containing stabilizers were first employed in batch
processes to prevent degradation and discoloration of the
polyethylene terephthalate polyester.
Although adding a stabilizer to the polymer melt in a batch reactor
is a relatively simple process, numerous problems arise if the
stabilizers are added in the continuous production of polyethylene
terephthalate. For example, while early addition of the stabilizer
prevents discoloration and degradation of the polyester, it also
causes reduced production throughput (i.e., decreases
polycondensation reaction rates). Moreover, such stabilizer is
typically dissolved in ethylene glycol, the addition of which
further slows the polymerization process. Consequently, early
addition of the stabilizer in the polymerization process requires
an undesirable choice between production throughput and thermal
stability of the polymer. As used herein, "thermal stability"
refers to a low rate of acetaldehyde generation, low discoloration,
and retention of molecular weight following subsequent heat
treatment or other processing.
Late addition of the stabilizer (e.g., after the polymerization
process during polymer processing) may provide insufficient
opportunity for the stabilizer to fully blend with the polymer.
Consequently, the stabilizer may not prevent degradation and
discoloration of the polyester. In addition, adding stabilizer
during polymer processing is inconvenient and does not provide
economies of scale.
U.S. Pat. No. 5,376,702 for a Process and Apparatus for the Direct
and Continuous Modification of Polymer Melts discloses dividing a
polymer melt stream into an unmodified stream and a branch stream
that receives additives. In particular, a side stream takes a
portion of the branch stream to an extruder, where additives are
introduced. Such techniques, however, are not only complicated, but
also costly, requiring a screw extruder and melt piping to process
additives. Consequently, such arrangements are inconvenient and
even impractical where total additive concentrations are low (e.g.,
less than one weight percent).
Certain problems associated with late addition of stabilizer are
addressed in U.S. Pat. No. 5,898,058 for a Method of
Post-Polymerization Stabilization of High Activity Catalysts in
Continuous Polyethylene Terephthalate Production, which discloses a
method of stabilizing high activity polymerization catalysts in
continuous polyethylene terephthalate production. This patent,
which is commonly assigned with this application, is hereby
incorporated entirely herein by reference.
In particular, U.S. Pat. No. 5,898,058 discloses adding a
stabilizer, which preferably contains phosphorous, at or after the
end of the polymerization reaction and before polymer processing.
This deactivates the polymerization catalyst and increases the
throughput of the polyester without adversely affecting the thermal
stability of the polyethylene terephthalate polyester. While a
noteworthy improvement over conventional techniques, U.S. Pat. No.
5,898,058 teaches adding the stabilizer without a carrier.
Consequently, the addition of solids into the polymer necessitates
the costly use of an extruder.
U.S. parent application Ser. No. 09/738,150 for Methods of
Post-Polymerization Injection in Continuous Polyethylene
Terephthalate Production, discloses a process for the production of
high quality polyethylene terephthalate polyester that improves
upon the stabilizer-addition techniques disclosed by
commonly-assigned U.S. Pat. No. 5,898,058.
More specifically, U.S. application Ser. No. 09/738,150 discloses a
method for the late introduction of additives into a process for
making polyethylene terephthalate. The additives are introduced
during, and preferably after, the polycondensation of polyethylene
terephthalate polymers. In particular, the method employs a
reactive carrier that not only functions as a delivery vehicle for
one or more additives, but also reacts with the polyethylene
terephthalate, thereby binding the carrier in the polyethylene
terephthalate resin. Moreover, U.S. application Ser. No. 09/738,150
discloses that this may be achieved using a simplified additive
delivery system that does not require the use of an extruder. (U.S.
application Ser. No. 09/932,150, for Methods of Post-Polymerization
Extruder Injection in Polyethylene Terephthalate Production, which
is a continuation-in-part of U.S. application Ser. No. 09/738,150,
discloses a method for late additive introduction at an extruder
during a process for making polyethylene terephthalate.)
The technology of U.S. application Ser. No. 09/738,150 is
effectively employed in co-pending and commonly-assigned
application U.S. Ser. No. 09/738,619 for Polyester Bottle Resins
Having Reduced Frictional Properties and Methods for Making the
Same, which was also filed Dec. 15, 2000, and which is herein
incorporated by reference in its entirety. U.S. application Ser.
No. 09/738,619, in certain preferred embodiments, likewise employs
a simplified additive delivery system that does not require the use
of an extruder.
The method of U.S. parent application Ser. No. 09/738,150 has
application to the production of condensation polymers generally.
There is, in fact, a need for a post-polymerization injection
technique that ensures that the late introduction of additives
during condensation polymer production will yield condensation
polymers whose additives and carriers are integral parts of the
polymer resin.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
method of adding additives to condensation polymers via a reactive
carrier after the melt-phase polycondensation reactions are
essentially complete.
It is a further object of the present invention to provide a method
of adding additives to condensation polymers via a reactive carrier
in order to reduce polymer transition times and eliminate process
upsets resulting from changing polymer formulations.
It is a further object of the present invention to provide a method
of introducing additives into condensation polymers in a way that
reduces the degradation or volatilization of such additives.
It is a further object of the present invention to provide a
simplified additive delivery system wherein the reactive carrier is
a pumpable liquid or slurry at or near room temperature.
It is a further object of the present invention to provide a
simplified additive delivery system that does not require the use
of an extruder to deliver additives.
It is a further object of the present invention to provide a
continuous process for the production of condensation polymers,
such as high-quality polyethylene terephthalate polyester, that
improves upon the stabilizer-addition techniques disclosed by
commonly-assigned U.S. Pat. No. 5,898,058.
The foregoing, as well as other objectives and advantages of the
invention and the manner in which the same are accomplished, is
further specified within the following detailed description and its
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the theoretical loss of molecular weight (as
measured by number-average degree of polymerization) for
condensation polymers having an initial degree of polymerization of
about 100 as a function of the concentration of the reactive
carrier at various molecular weights.
FIG. 2 illustrates the theoretical loss of molecular weight (as
measured by number-average degree of polymerization) for
condensation polymers having an initial degree of polymerization of
about 70 as a function of the concentration of the reactive carrier
at various molecular weights.
FIG. 3 illustrates the theoretical loss of intrinsic viscosity of
polyethylene terephthalate having an intrinsic viscosity of 0.63
dl/g as a function of the concentration of the reactive carrier at
various molecular weights.
FIG. 4 illustrates the theoretical loss of intrinsic viscosity of
polyethylene terephthalate having an intrinsic viscosity of 0.45
dl/g as a function of the concentration of the reactive carrier at
various molecular weights.
DETAILED DESCRIPTION
The invention is a novel method for the late introduction of
additives into a process for making condensation polymers. The
additives are introduced during, and preferably after,
polycondensation. In particular, the method employs a reactive
carrier that not only functions as a delivery vehicle for one or
more additives, but also reacts with the condensation polymers,
thereby binding the reactive carrier in the polymer resin. This
prevents the emergence of the reactive carrier from the
condensation polymers during subsequent processing, such as solid
state polymerization, drying operations, spinning operations, film
extrusion, and injection molding operations. This also improves
dispersion of the additive in the condensation polymers and reduces
the tendency of the carrier to deposit in polymer processing
equipment during solid state polymerization.
Accordingly, in a preferred embodiment, the present invention
includes polymerizing oligomeric precursors via melt phase
polycondensation to form condensation polymers having carbonyl
functionality. Thereafter, one or more additives are introduced
into the condensation polymers by way of a reactive carrier that
has a molecular weight of less than about 10,000 g/mol.
In another preferred embodiment, the invention includes
polymerizing oligomeric precursors via melt phase polycondensation
to form condensation polymers having carbonyl functionality and a
target average degree of polymerization of at least about 70. Then,
after the condensation polymers have achieved this target degree of
polymerization, one or more additives are introduced into the
condensation polymers by way of a reactive carrier having a
molecular weight of less than about 10,000 g/mol. Thereafter, the
melt phase polycondensation of the condensation polymers is
completed.
Where additives are introduced during polycondensation, the target
average degree of polymerization is preferably at least about 80,
more preferably at least about 90, and most preferably at least
about 100. At an average degree of polymerization of at least about
70, the condensation polymers develop chain entanglements that
result in useful properties, such as melt strength, impact
resistance, and modulus. It will be understood by those of ordinary
skill in the polymer arts that the embodiments of the present
invention as herein disclosed are applicable regardless of whether
the late addition of additives occurs after the polycondensation
stage or during the polycondensation stage (i.e., where target
average degree of polymerization of the condensation polymers is at
least about 70).
As used herein, the term "carbonyl functionality" refers to a
carbon-oxygen double bond that is an available reaction site.
Condensation polymers having carbonyl functionality are typically
characterized by the presence of a carbonyl functional group (i.e.,
C.dbd.O) with at least one adjacent hetero atom (e.g., an oxygen
atom, a nitrogen atom, or a sulfur atom) functioning as a linkage
within the polymer chain. Accordingly, "carbonyl functionality" is
meant to embrace various functional groups including, without
limitation, esters, amides, imides, carbonates, and urethanes.
Suitable polycondensation polymers according to the present
invention include, without limitation, polyesters, polyurethanes,
polycarbonates, polyamides, and polyimides. Polyesters, such as
polyethylene terephthalate, polytrimethylene terephthalate,
polybutylene terephthalate, are preferred.
As will be understood by those of ordinary skill in the art,
oligomeric precursors to condensation polymers may be formed by
reacting a first polyfunctional component and a second
polyfunctional component. For example, oligomeric precursors to
polycarbonates may be formed by reacting diols and derivatives of
carbonic acid, oligomeric precursors to polyurethanes may be formed
by reacting diisocyanates and diols, oligomeric precursors to
polyamides may be formed by diacids and diamines and oligomeric
precursors to polyimides may be formed by reacting dianhydrides and
diamines. See, e.g., Odian, Principles of Polymerization, (Second
Edition 1981). These kinds of reactions are well understood by
those of ordinary skill in the polymer arts and will not be further
discussed herein.
It will be further understood by those having ordinary skill in the
art that certain monomers possessing multi-functionality can
self-polymerize to yield condensation polymers. For example, amino
acids and nylon salts are each capable of self-polymerizing into
polyamides, and hydroxy acids (e.g., lactic acid) can
self-polymerize into polyesters (e.g., polylactic acid).
Polyesters are the preferred polycondensation polymers, and so the
present invention is herein described with particular reference to
the introduction of additives into a process for making
polyethylene terephthalate. In this regard, oligomeric precursors
to polyesters may be formed by reacting diacids and diols or by
reacting diesters and diols. The diols may be either aliphatic or
aromatic.
It will be apparent to those of ordinary skill in the polymer arts
that the description of the present invention is directed not only
to the introduction of additives into polyethylene terephthalate,
but also to the introduction of additives into any condensation
polymer that possesses carbonyl functionality along its polymer
chain. It is expected that an exemplary description of the
invention using a preferred condensation polymer (i.e.,
polyethylene terephthalate) will enable those skilled in the
polymer arts to practice, without undue experimentation, the
invention for any condensation polymer having carbonyl
functionality. In this regard, those having ordinary skill in the
polymer arts will recognize that there are numerous kinds of
condensation polymers and copolymers that can be synthesized
without departing from the scope and spirit of the present
invention.
The invention preferably includes reacting a terephthalate
component and a diol component to form polyethylene terephthalate
precursors, e.g., bis(2-hydroxyethyl)terephthalate. These
oligomeric precursors are then polymerized via melt phase
polycondensation to form polymers of polyethylene terephthalate.
During polycondensation, which is usually enhanced by catalysts,
ethylene glycol is continuously removed to create favorable
reaction kinetics. Thereafter, one or more additives are introduced
by way of a reactive carrier into the polyethylene terephthalate
polymers (i.e., the reactive carrier functions as an additive
delivery vehicle). The reactive carrier, which, as noted, has a
molecular weight of less than about 10,000 g/mol, not only
facilitates uniform blending of the additives within the polymer
melt, but also reacts with the polyethylene terephthalate polymers
to ensure that the carrier does not emerge during subsequent
processes.
Another aspect of the invention includes polymerizing the
polyethylene terephthalate precursors via melt phase
polycondensation to form polyethylene terephthalate polymers having
a target intrinsic viscosity of at least about 0.45 dl/g (i.e., an
average degree of polymerization of about 70). Once the
polyethylene terephthalate polymers have achieved this target
intrinsic viscosity, one or more additives are introduced by way of
a reactive carrier having a molecular weight of less than about
10,000 g/mol. Finally, the melt phase polycondensation of the
polyethylene terephthalate polymers is completed. Where additives
are introduced during the polycondensation of polyethylene
terephthalate polymers, the target intrinsic viscosity is
preferably at least about 0.50 dl/g, more preferably at least about
0.55 dl/g, and most preferably at least about 0.60 dl/g (i.e.,
average degrees of polymerization of about 80, 90, and 100,
respectively). At an intrinsic viscosity of at least about 0.45
dl/g, the polyethylene terephthalate polymer possesses sufficient
molecular weight, mechanical properties, melt strength, and
crystallinity to facilitate polymer processing.
As used herein, the term "intrinsic viscosity" is the ratio of the
specific viscosity of a polymer solution of known concentration to
the concentration of solute, extrapolated to zero concentration.
Intrinsic viscosity, which is widely recognized as standard
measurements of polymer characteristics, is directly proportional
to average polymer molecular weight. See, e.g., Dictionary of Fiber
and Textile Technology, Hoechst Celanese Corporation (1990);
Tortora & Merkel, Fairchild's Dictionary of Textiles (7.sup.th
Edition 1996).
Intrinsic viscosity can be measured and determined without undue
experimentation by those of ordinary skill in this art. For the
intrinsic viscosity values described herein, the intrinsic
viscosity is determined by dissolving the copolyester in
orthochlorophenol (OCP), measuring the relative viscosity of the
solution using a Schott Autoviscometer (AVS Schott and AVS 500
Viscosystem), and then calculating the intrinsic viscosity based on
the relative viscosity. See, e.g., Dictionary of Fiber and Textile
Technology ("intrinsic viscosity").
In particular, a 0.6-gram sample (+/-0.005 g) of dried polymer
sample is dissolved in about 50 ml (61.0-63.5 grams) of
orthochlorophenol at a temperature of about 105.degree. C. Fiber
and yarn samples are typically cut into small pieces, whereas chip
samples are ground. After cooling to room temperature, the solution
is placed in the viscometer at a controlled, constant temperature,
(e.g., between about 20.degree. C. and 25.degree. C.), and the
relative viscosity is measured. As noted, intrinsic viscosity is
calculated from relative viscosity.
The term "diol component" herein refers primarily to ethylene
glycol, although other diols (e.g., low molecular weight
polyethylene glycol) may be used as well. It will be understood by
those of ordinary skill in the art that the diol component usually
forms the majority of terminal ends of the polymer chains and so is
present in the composition in slightly greater fractions. For
example, the molar ratio of the terephthalate component and the
diol component is typically between about 1.0:1.0 and 1.0:1.6.
The term "terephthalate component" herein refers to diacids and
diesters that can be used to prepare polyethylene terephthalate. In
particular, the terephthalate component mostly includes
terephthalic acid and dimethyl terephthalate, but can include
diacid and diester comonomers as well. In this regard, those having
ordinary skill in the art will know that there are two conventional
methods for forming polyethylene terephthalate. These methods are
well known to those skilled in the art.
One method employs a direct esterification reaction using
terephthalic acid and excess ethylene glycol. In this technique,
the aforementioned step of reacting a terephthalate component and a
diol component includes reacting terephthalic acid and ethylene
glycol in a heated esterification reaction to form monomers and
oligomers of terephthalic acid and ethylene glycol, as well as a
water byproduct. To enable the esterification reaction to go
essentially to completion, the water must be continuously removed
as it is formed.
The other method involves a two-step ester exchange reaction and
polymerization using dimethyl terephthalate and excess ethylene
glycol. In this technique, the aforementioned step of reacting a
terephthalate component and a diol component includes reacting
dimethyl terephthalate and ethylene glycol in a heated ester
exchange reaction to form monomers and oligomers of terephthalate
and ethylene glycol, as well as methanol as a byproduct. To enable
the ester exchange reaction to go essentially to completion, the
methanol must be continuously removed as it is formed.
It will be understood by those having ordinary skill in the art
that the polyethylene terephthalate herein described may be a
modified polyethylene terephthalate to the extent the diol
component includes other glycols besides ethylene glycol, such as
diethylene glycol, 1,3-propanediol, 1,4-butanediol and
1,4-cyclohexane dimethanol, or the terephthalate component includes
modifiers such as isophthalic acid, 2,6-naphthalene dicarboxylic
acid, succinic acid, or one or more functional derivatives of
terephthalic acid. In fact, most commercial polyethylene
terephthalate polymers are modified polyethylene terephthalate
polyesters.
In the present invention, the direct esterification reaction is
preferred over the older, two-step ester exchange reaction. As
noted, the direct esterification technique reacts terephthalic acid
and ethylene glycol to form low molecular weight monomers,
oligomers, and water.
For example, in a typical process, the continuous feed enters a
direct esterification vessel that is operated at a temperature of
between about 240.degree. C. and 290.degree. C. and at a pressure
of between about 5 and 85 psia for between about one and five
hours. The reaction, which is typically uncatalyzed, forms low
molecular weight monomers, oligomers, and water. The water is
removed as the esterification reaction proceeds and excess ethylene
glycol is removed to provide favorable reaction kinetics.
Thereafter, the low molecular weight monomers and oligomers are
polymerized via polycondensation to form polyethylene terephthalate
polyester. This polycondensation stage generally employs a series
of two or more vessels and is operated at a temperature of between
about 250.degree. C. and 305.degree. C. for between about one and
four hours. The polycondensation reaction usually begins in a first
vessel called the low polymerizer. The low polymerizer is operated
at a pressure range of between about 0 and 70 torr. The monomers
and oligomers polycondense to form polyethylene terephthalate and
ethylene glycol.
As noted previously, the ethylene glycol is removed from the
polymer melt using an applied vacuum to drive the reaction to
completion. In this regard, the polymer melt is typically agitated
to promote the escape of the ethylene glycol from the polymer melt
and to assist the highly viscous polymer melt in moving through the
polymerization vessel.
As the polymer melt is fed into successive vessels, the molecular
weight and thus the intrinsic viscosity of the polymer melt
increases. The temperature of each vessel is generally increased
and the pressure decreased to allow greater polymerization in each
successive vessel.
The final vessel, generally called the "high polymerizer," is
operated at a pressure of between about 0 and 40 torr. Like the low
polymerizer, each of the polymerization vessels is connected to a
flash vessel and each is typically agitated to facilitate the
removal of ethylene glycol. The residence time in the
polymerization vessels and the feed rate of the ethylene glycol and
terephthalic acid into the continuous process is determined in part
based on the target molecular weight of the polyethylene
terephthalate polyester. Because the molecular weight can be
readily determined based on the intrinsic viscosity of the polymer
melt, the intrinsic viscosity of the polymer melt is generally used
to determine polymerization conditions, such as temperature,
pressure, the feed rate of the reactants, and the residence time
within the polymerization vessels.
Note that in addition to the formation of polyethylene
terephthalate polymers, side reactions occur that produce
undesirable by-products. For example, the esterification of
ethylene glycol forms diethylene glycol (DEG), which is
incorporated into the polymer chain. As is known to those of skill
in the art, diethylene glycol lowers the softening point of the
polymer. Moreover, cyclic oligomers (e.g., trimer and tetramers of
terephthalic acid and ethylene glycol) may occur in minor amounts.
The continued removal of ethylene glycol as it forms in the
polycondensation reaction will generally reduce the formation of
these by-products.
Although the foregoing discussion concentrates upon the continuous
production of polyester terephthalate polymers, it will be
understood that the invention is not so limited. The teachings
disclosed herein may be applied to other polycondensation polymers
using continuous processes, semi-continuous processes, and even
batch processes.
For instance, the condensation polymers of the present invention
are generally filtered and extruded in the melt phase to form
polymer sheets, filaments, or pellets. Preferably, the polymer melt
is extruded immediately after polycondensation. After extrusion,
the polymers are quenched, preferably by spraying with water or
immersing in a water trough, to promote solidification. The
solidified condensation polymers are cut into chips or pellets for
storage and handling purposes. As used herein, the term "pellets"
is used generally to refer to chips, pellets, and the like.
As will be known to those of ordinary skill in the art, the pellets
formed from the condensation polymers and the reactive carrier, in
some circumstances, may be subjected to crystallization followed by
solid state polymerization (SSP) to increase the molecular weight
of the polymer resin. It should be noted that the method of the
invention does not adversely affect the SSP rate and often will
even increase the SSP rate. The polymer chips are then re-melted
and re-extruded to form items such as containers (e.g., beverage
bottles), filaments, films, or other applications. Those of
ordinary skill in the art will recognize that certain condensation
polymers, such as amorphous polycarbonate, need not undergo
SSP.
A particular advantage of the present invention is the reduction of
polymer transition times and elimination of upsets to continuous
processes that result from polymer formulation changes. For
example, conventional polyester processing introduces additives in
an ethylene glycol solution or slurry. These ethylene glycol
streams are added into the esterification process or the first
polycondensation vessel, each of which have a high ethylene glycol
content. To effect a product change, the contents of each
subsequent vessel must be completely replaced. In standard
continuous units, the required transition time is on the order of
four to eight hours.
The present invention improves upon the prior art by employing a
reactive carrier rather than an inert carrier or no carrier at all.
The reactive carrier should be introduced to the condensation
polymers in quantities such that bulk polymer properties are not
significantly affected. The reactive carrier preferably is capable
of combining with the condensation polymers such that it is
non-extractable during subsequent processing operations.
Preferably, the reactive carrier has a melting point that ensures
that it is a liquid or slurry at about 100.degree. C., which can be
achieved using low-pressure steam. Most preferably, the reactive
carrier has a melting point that ensures that it is a liquid or
slurry at near ambient temperatures. As used herein, the term "near
ambient" includes temperatures between about 20.degree. C. and
60.degree. C. Near ambient temperatures simplify the unit
operations necessary to introduce additives. Neither extruders nor
complicated heating systems are needed to introduce the reactive
carrier into the condensation polymers.
As a general matter, the reactive carrier should make up no more
than about one weight percent of the polymer resin (i.e., 10,000
ppm). Preferably, the reactive carrier is introduced to the
condensation polymers in quantities such that its concentration in
the polymer resin is less than about 1000 ppm (i.e., 0.1 weight
percent). Reducing the reactive carrier to quantities such that its
concentration in the polymer resin is less than 500 ppm (i.e., 0.05
weight percent) will further reduce potential adverse effects to
bulk polymer properties.
FIGS. 1 and 2 illustrate the theoretical loss of molecular weight
(as measured by number-average degree of polymerization) as a
function of the concentration of the reactive carrier at various
molecular weights. FIG. 1 depicts the impact of the reactive
carrier upon condensation polymers that have an initial degree of
polymerization of about 100. Similarly, FIG. 2 depicts the impact
of the reactive carrier upon condensation polymers that have an
initial degree of polymerization of about 70. (For polyethylene
terephthalate, degree of polymerization of about 100 corresponds to
an intrinsic viscosity of about 0.61 dl/g and a degree of
polymerization of about 70 corresponds to an intrinsic viscosity of
about 0.45 dl/g.) Note that at any concentration in a condensation
polymer resin, the reactive carriers having higher molecular
weights have less adverse effect upon the polymer resin's average
degree of polymerization.
Similarly, FIGS. 3 and 4 illustrate the theoretical loss of
intrinsic viscosity as a function of reactive carrier concentration
at several molecular weights. FIG. 3 depicts the impact of the
reactive carrier upon polyethylene terephthalate having an
intrinsic viscosity of 0.63 dl/g. Similarly, FIG. 4 depicts the
impact of the reactive carrier upon polyethylene terephthalate
having intrinsic viscosity of 0.45 dl/g.
As will be understood by those of ordinary skill in the art,
macromolecules having a degree of polymerization of about 70 are
considered high polymers. For polyethylene terephthalate, this
roughly translates to a molecular weight of at least about 13,000
g/mol. At this molecular weight, polyethylene terephthalate
polymers possess sufficient molecular weight, mechanical
properties, melt strength, and crystallinity to facilitate polymer
processing.
In contrast, the reactive carriers according to the present
invention have molecular weights that are less than about 10,000
g/mol. The molecular weight of the reactive carrier is typically
less than 6000 g/mol, preferably less than 4000 g/mol, more
preferably between about 300 and 2000 g/mol, and most preferably
between about 400 and 1000 g/mol. As used herein, molecular weight
refers to number-average molecular weight, rather than
weight-average molecular weight.
In general, reactive carriers having carboxyl, hydroxyl, or amine
functional groups are favored. Suitable reactive carriers include
esters (including low polymers derived from caprolactone), amides
(including low polymers derived from caprolactam), imides, amines,
isocyanates, oxazolines, acids, and anhydrides that are capable of
reacting with the condensation polymers during solid state
polymerization and not causing the condensation polymers to suffer
loss of molecular weight during subsequent heated processes, such
as injection molding and extrusion operations.
Also preferred are polyols, especially polyester polyols and
polyether polyols, having a molecular weight that is sufficiently
high such that the polyol will not substantially reduce the average
molecular weight of the condensation polymers, and a viscosity that
facilitates pumping of the polyol. Polyethylene glycol is a
preferred polyol. Other exemplary polyols include functional
polyethers, such as polypropylene glycol that is prepared from
propylene oxide, random and block copolymers of ethylene oxide and
propylene oxide, and polytetramethylene glycol that is derived from
the polymerization of tetrahydrofuran.
Alternatively, the reactive carrier may also include dimer or
trimer acids and anhydrides. In another embodiment, the reactive
carrier may possess, in addition to or in place of terminal
functional groups, internal functional groups (e.g., esters,
amides, and anhydrides) that react with the condensation polymers.
In yet another embodiment, the reactive carrier may include esters
without terminal functional groups, amides without terminal
functional groups, or anhydrides without terminal functional groups
that are capable of reacting into the condensation polymers during
solid state polymerization and that will not cause the condensation
polymers to suffer loss of molecular weight during injection
molding or extrusion processes. As noted and as will be appreciated
by those having ordinary skill in the art, reactive carriers
derived from suitable heterocycles (e.g., caprolactone and
caprolactam) are within the scope of the present invention.
It should be recognized that additives are sometimes marketed with
oligomers that constitute an acceptable reactive carrier. For
example, TINUVIN.RTM. 213, which is available from Ciba Specialty
Chemicals, includes a hydroxyphenyl benzotriazole ultraviolet light
absorber in a solution of unreacted polyethylene glycol having a
molecular weight of 300 g/mol. As discussed previously,
polyethylene glycol is a preferred reactive carrier. Accordingly,
the present invention embraces the use of such premixed,
additive/reactive carrier products.
An exemplary method according to the present invention includes
reacting terephthalic acid and ethylene glycol in a heated
esterification reaction to form monomers and oligomers of
terephthalic acid and ethylene glycol, then polymerizing these
monomers and oligomers via melt phase polycondensation to form
polyethylene terephthalate polymers. Thereafter, an additive is
introduced into the polyethylene terephthalate polymers using a
reactive carrier, which facilitates uniform blending within the
polymer melt. Preferably, the reactive carrier is a polyol (e.g.,
polyethylene glycol) having a molecular weight that permits the
polyol to be pumped at near ambient temperatures (i.e., less than
60.degree. C.) and that is introduced to the polyethylene
terephthalate polymers in quantities such that bulk properties of
the polyethylene terephthalate polymers are not significantly
affected. The polyethylene terephthalate polymers are then formed
into chips (or pellets via a polymer cutter) before being solid
state polymerized. Importantly, the polyol reactive carrier
combines with the polyethylene terephthalate polymer such that it
is non-extractable during subsequent processing operations (e.g.,
forming polyester beverage containers).
As noted, the invention embraces the late addition of various kinds
of additives via the reactive carrier. Late addition is especially
desirable where the additives are volatile or subject to thermal
degradation. Conventional additive injection prior to
polycondensation, such as during an esterification stage in the
synthesis of polyester, or early during the polycondensation stage
subjects additives to several hours of high-temperature (greater
than 260.degree. C.) and reduced-pressure (less than 10 torr)
conditions. Consequently, additives that have significant vapor
pressure at these conditions will be lost from the process.
Advantageously, the method of the present invention significantly
reduces the time additives are exposed to high polycondensation
temperatures.
Additives according to the present invention can include preform
heat-up rate enhancers, friction-reducing additives, stabilizers,
inert particulate additives (e.g., clays or silicas), colorants,
antioxidants, branching agents, oxygen barrier agents, carbon
dioxide barrier agents, oxygen scavengers, flame retardants,
crystallization control agents, acetaldehyde reducing agents,
impact modifiers, catalyst deactivators, melt strength enhancers,
anti-static agents, lubricants, chain extenders, nucleating agents,
solvents, fillers, and plasticizers.
In a preferred embodiment, the additive is an ultraviolet (UV)
radiation absorber. As is understood by those familiar with
polyester packaging, UV absorbers protect the polyethylene
terephthalate polymers and contents of packages from UV
degradation.
In another preferred embodiment, the additive is an inert
particulate additive, preferably either talc (i.e., a natural
hydrous magnesium silicate of representative formula
3MgO.4SiO.sub.2.H.sub.2 O) or precipitated calcium carbonate. The
inert particulate additive is introduced in low concentrations
(i.e., about 20 and 200 ppm based on the combined weight of the
condensation polymers, the reactive carrier, and the inert
particulate additive) to ensure that bottles formed from the
condensation polymers possess reduced frictional characteristics.
Moreover, the inert particulate additive, which is preferably
surface-treated to minimize haze formation in bottles, preferably
has an average particle size of less than about ten microns, more
preferably less than two microns. As described in
commonly-assigned, copending U.S. Ser. No. 09/738,619, bottles
formed from such polyethylene terephthalate condensation polymers
have improved frictional characteristics that reduce, and can
eliminate, the need to apply, during filling operations, external
lubricants to polyester bottles.
In another preferred embodiment, the additive is an exfoliated clay
nanocomposite, which enhances gas barrier properties in films and
containers. Nanocomposites preferably are in the form of platelets
having a thickness of between about 6 and 15 angstroms.
As will be known by those having skill in the art, polymerization
catalysts increase polymerization rates, and thus productivity.
Unfortunately, these same catalysts will eventually degrade the
thermal stability of the polymer resin. Thus, in yet another
preferred embodiment, the additive carried by the reactive carrier
is a catalyst stabilizer. While phosphorous-containing stabilizers
are preferred, any stabilizer that will deactivate the
polymerization catalyst may be introduced via a reactive carrier.
In general, the stabilizer should be non-reactive with the polymer
and possess low residual moisture.
U.S. parent application Ser. No. 09/738,150 explains that as the
polycondensation reaction of polyethylene terephthalate nears
completion, the catalyst begins to form acetaldehyde and cause
discoloration or yellowing of the polyethylene terephthalate.
Accordingly, as discussed herein, thermally stable polyester refers
to polyester having low acetaldehyde content, low discoloration,
and high retention of molecular weight despite exposure to high
temperatures.
Acetaldehyde is an objectionable byproduct of polyethylene
terephthalate degradation. This is of particular concern to the
food and beverage industry because acetaldehyde, even in minute
amounts, adversely affects product taste. Moreover, polymer
degradation will typically cause undesirable discoloration or
yellowing. This is why a stabilizer, preferably containing
phosphorous, is added to the polymer melt.
Advantageously, the late addition of the stabilizer to the polymer
melt prevents the stabilizer from inhibiting ("cooling") the
polymerization catalyst during the polycondensation reaction. This
increases the production efficiency of continuous polyethylene
terephthalate processes. Furthermore, because the stabilizer is
added before polymer processing, the stabilizer can adequately
prevent discoloration and degradation of the polyethylene
terephthalate polyester.
Finally, it should be noted that because the melting and extruding
steps in the formation of the condensation polymers are performed
at elevated temperatures (e.g., usually greater than 260.degree. C.
for polyethylene terephthalate), it is important that the
condensation polymers be thermally stable. Accordingly, the
stabilizer additive must be adequately blended with the polymer
melt to deactivate polymerization catalysts. The reactive carrier
facilitates the incorporation of the stabilizer into the polymer
resin.
In the specification and the drawings, typical embodiments of the
invention have been disclosed. Specific terms have been used only
in a generic and descriptive sense, and not for purposes of
limitation. The scope of the invention is set forth in the
following claims.
* * * * *